For example, PTL 1 discloses an information display device that optically modulates laser light from a laser light source based on display information using an optical modulator and then inputs the modulated laser light to a deflector. Next, the deflector guides the light reflected and deflected in the y-axis direction to another deflector, and another deflector 4 two-dimensionally scans the light reflected and deflected in the x-axis direction on the surface of a screen such as, for example, a diffusion screen or directivity-limited screen. In addition, PTL 1 discloses, for example, a rotatable mirror, a galvanometer mirror, and a rotatable polygon mirror as such deflectors and display information is reflected to the screen by rotation or vibration of such deflectors. In addition, PTL 1 discloses an information display device having such a screen on the wind shield (front glass) of a vehicle, as a head-up display device for vehicles.
Next, for example, PTL 2 discloses an image display device in which a light source unit emits red light, green light, blue light, or light (compound light) obtained by combining these types of light to a collimating optical system and then the collimated image light is input to a horizontal scan unit. The horizontal scan unit horizontally scans the image light at high speed and guides the image light to a vertical scan unit via a relay optical system. The vertical scan unit vertically scans the image light at high speed. An eyepiece optical system (another relay optical system) guides the two-dimensionally scanned image light to the user's eyes (pupils). In addition, for example, PTL 2 discloses, for example, a galvanometer mirror or the like as such a scan unit. Such an image display device is generally referred to as a head mounted display (HMD) by those skilled in the art.
Next, for example, PTL 3 discloses an image display device for vehicles that is capable of displaying, on the wind shield, information concerning actual scene so that the virtual image of the information is superimposed on actual scene from the viewpoint of the driver of the vehicle. As a display unit for displaying or projecting such information onto the wind shield, a two-dimensional scan system including two deflectors and two scan units described above is generally adopted.